Hi Steve, I don't know what colour wires are used in the eight pin cable but here's a diagram that should show where the ends of them connect, assuming it's wired internally the same as mine:
To check the +5V supply, put the black probe from your meter onto the battery negative (-) connection and set your meter to a DC volt range that is high enough to measure your battery voltage, just in case you touch the battery positive (+) wire by mistake, and then use a pin or paper-clip held against the red meter probe to gently touch the +5V contact inside the 8 pin socket. Don't push the paper-clip/pin right in, because it could open up the metal contact too far, resulting in a very loose and poor connection when the correct plug is inserted again.
Alan